. PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 5939 
would absorb in 24 hours; and secondly the alteration effected upon them by 
the action of moist carbonic acid. 
It was found that— 






Contained of - 
Specific Gravity. eae ae Water, nee oe on 
| Ardshiel granite, 2° 774 04 +139 
Furness granite, 2° 603 * 626 282 
| Bunawe granite, 2° 662 “241 -18 
Ratho “greenstone,” . 2° 882 ly 162 1+ 52 
Marchburn “ greenstone,” 2G °059 *031 
Knockdow “greenstone,” . ; f 2 O97 062 029 




Here there is the power of taking into their pores the instrument of change. 
___ Intesting the power of that instrument, the following process was adopted :— 
One ounce of coarsely pulverised fragments of the rock were suspended in four 
ounces of water by the agitation of a current of carbonic acid, which was passed 
through them for two and a half hours. 
_ This treatment was found to dissolve of the Knockdow greenstone 1°1 per 
cent., of which ‘0475 was silica; = 4°32 per cent. of what was dissolved. 
Of the Ratho stone there were dissolved 0° 895 per cent., of which ‘04 was 
silica; = 4°47 per cent. 
As it is a recognised fact that silica is less soluble in carbonated than in 
ordinary water, this rapid solubility in the acidified water shows how great must 
be the solubility in ordinary waters. 
The substances which were found to make up the remainder of the portion 
dissolved were the alkalies, lime, and iron ; the latter becoming peroxidised 
rapidly and totally during the evaporation of the solution. 
The point of chief moment was that only traces of magnesia appeared in 
the solution. 
It was Biscuor who first clearly pointed out the potency of carbonated 
Waters in effecting decomposition of rocks containing the substances above noted 
as soluble therein ; and its absolute want of power to remove magnesia from 
them on account of the insolubility of silicate of magnesia in carbonated waters 
or even in carbonated alkalies, supposing these to be formed as a first step in 
such a process. 
Hence the direct and unfailing action of such waters upon augitic rocks 
must be their conversion into serpentine. 
It has been shown that inasmuch as carbonic acid does not combine with 
alumina it can have no power to remove that alumina; and so a serpentine 
